Gray has written several influential books, including False Dawn: The Delusions of Global Capitalism (1998), which argues that free market globalization is an unstable Enlightenment project currently in the process of disintegration, Straw Dogs: Thoughts on Humans and Other Animals (2003), which attacks philosophical humanism, a worldview which Gray sees as originating in religious ideologies, and Black Mass: Apocalyptic Religion and the Death of Utopia (2007), a critique of utopian thinking in the modern world. Gray sees volition, and hence morality, as an illusion, and portrays humanity as a ravenous species engaged in wiping out other forms of life. Gray writes that 'humans ... cannot destroy the Earth, but they can easily wreck the environment that sustains them.'[2]

Gray's political thought is famous for its mobility across the political spectrum over the years. As a student, Gray was on the left and continued to vote Labour into the mid-1970s; by 1976 he had shifted towards a right-liberal New Right position, convinced that the world was changing irrevocably through technological inventions, realigned financial markets and new economic power blocs, and that the left failed to comprehend the magnitude and nature of this change.[7] In the 1990s Gray became an advocate for environmentalism and New Labour. Gray considers the conventional (left-wing/right-wing) political spectrum of conservatism and social democracy as no longer viable.[8]

Central to the doctrine of humanism, in Gray’s view, is the inherently utopian belief in meliorism, namely that humans are not limited by their biological natures and that advances in ethics and politics are cumulative or that they can alter or improve the human condition, in the same way that advances in science and technology have altered or improved living standards.[9]

Gray contends, in opposition to this view, that history is not progressive, but cyclical. Human nature, he argues, is an inherent obstacle to cumulative ethical or political progress.[9] Seeming improvements, if there are any, can very easily be reversed: one example he has cited has been the use of torture by the United States against terrorist suspects.[10][11] "What's interesting," Gray said in an interview in 032c magazine, "is that torture not only came back, but was embraced by liberals, and defended by liberals. Now there are a lot of people, both liberal and conservative, who say, 'Well, it's a very complicated issue.' But it wasn't complicated until recently. They didn't say that five or ten years ago."[12]

Furthermore, he argues that this belief in progress, commonly imagined to be secular and liberal, is in fact derived from an erroneous Christian notion of humans as morally autonomous beings categorically different from other animals. This belief, and the corresponding idea that history makes sense, or is progressing towards something, is in Gray’s view merely a Christian prejudice.[9]

In Straw Dogs, he argues that the idea that humans are self-determining agents does not pass the acid test of experience. Those Darwinist thinkers who believe humans can take charge of their own destiny to prevent environmental degradation are, in this view, not naturalists, but apostles of humanism.[9]

He identifies the Enlightenment as the point at which the Christian doctrine of salvation was taken over by secular idealism and became a political religion with universal emancipation as its aim.[9]Communism, fascism and "global democratic capitalism" are characterised by Gray as Enlightenment 'projects' which have led to needless suffering, in Gray's view, as a result of their ideological allegiance to this religion.[13]

The term agonistic liberalism appears in John Gray's book Isaiah Berlin from 1995. Gray uses this phrase to describe what he believes is Berlin's theory of politics, namely his support for both value pluralism and liberalism.

More generally, agonistic liberalism could be used to describe any kind of liberalism which claims that its own value commitments do not form a complete vision of politics and society, and that one instead needs to look for what Berlin calls an "uneasy equilibrium" between competing values. Under Gray's understanding, many contemporary liberal theorists would fall in this category, for instance John Rawls and Karl Popper.

Agonistic liberalism is an alternative to Berlin's theory of value pluralism and liberalism. While Berlin claimed equal validity for conflicting liberal views, agonistic liberalism holds that over time solutions may be found that determines which values are correct.[14]

Agonistic liberalism is the theory that conflict rather than discussion is the basis of social change.[15]

He has discussed James Lovelock's new ideas on evolution's next step; a species beyond human species that will be better able to co-exist with other species on this planet in the distant future.

His 1998 book False Dawn was praised by George Soros as "a powerful analysis of the deepening instability of global capitalism" which "should be read by all who are concerned about the future of the global economy".[19] John Banville praised Black Mass, saying that 'Gray's assault on Enlightenment ideas of progress is timelier than ever'.[21]

His 2002 book Straw Dogs: Thoughts on Humans and Other Animals has received particular praise. J. G. Ballard wrote that the book "challenges most of our assumptions about what it means to be human, and convincingly shows that most of them are delusions" and described it "a powerful and brilliant book", "an essential guide to the new millennium" and "the most exhilarating book I have read since Richard Dawkins's The Selfish Gene."[22] Self called the book "a contemporary work of philosophy devoid of jargon, wholly accessible, and profoundly relevant to the rapidly evolving world we live in" and wrote "I read it once, I read it twice and took notes. I arranged to meet its author so I could publicise the book – I thought it that good."[16][22]

Gray’s Straw Dogs has been criticised by Terry Eagleton, who has written: "mixing nihilism and New Ageism in equal measure, Gray scoffs at the notion of progress for 150 pages before conceding that there is something to be said for anaesthetics. The enemy in his sights is not so much a Straw Dog as a Straw Man: the kind of starry-eyed rationalist who passed away with John Stuart Mill, but who he has to pretend still rules the world".[24]Danny Postel also took issue with Straw Dogs. Postel stated Gray's claim that environmental destruction was the result of humanity's flawed nature, would be "welcome news to the captains of industry and the architects of the global economy; the ecological devastation they leave in their wake, according to Gray, has nothing to do with their exploits."[25] Postel also claimed that too much of Straw Dogs rested on "blanket assertion", and criticised Gray's use of the term "plague of people" as an outdated " neo-Malthusian persiflage about overpopulation".[25] Postel strongly condemned Gray for outlining "complete political passivity. There is no point whatsoever in our attempting to make the world a less cruel or more livable place."[25]